Solar panel disconnect and reactivation system

ABSTRACT

A photovoltaic system with an inverter, at least one solar panel for providing electrical power, and electrical wiring for coupling electrical power from the at least one solar panel to the inverter. Also included is a transmitter for transmitting a messaging protocol along the electrical wiring, where the protocol includes a multibit wireline signal. Also included is circuitry for selectively connecting the electrical power from the at least one solar panel along the electrical wiring to the inverter in response to the messaging protocol.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/087,216, filed Mar. 31, 2016, which is hereby incorporated byreference herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

BACKGROUND OF THE INVENTION

The preferred embodiments relate to solar panel systems and, moreparticularly, to disconnecting or reactivating connectivity of suchpanels to a power grid, for instance in connection with safetyconsiderations.

Solar panel electrical technology dates back many decades to thediscovery of the photovoltaic (PV) (i.e., solar) cell, but economic andecologic factors are now advancing the merits of larger scale use ofsuch technologies. As a result, solar panel systems are becoming moreefficient, cost-effective, and prolific. With such advancements, aspectsof solar panel systems are constantly being considered and improved,with the development of requirements or standards by certain governingbodies. In this regard, the National Electrical Code (NEC) is aregionally adoptable standard for the safe installation of variouselectrical equipment, which is commonly adopted in states ormunicipalities in the United States. The NEC has issued requirements forsafety considerations in environments where PV systems are installed, soas to reduce electric shock and energy hazards for emergency personnel,such as first responders and others, who may need to work in thevicinity of a PV system. For example, NEC requirements are provided forPVRSE (PV Rapid Shutdown Equipment) and PVRSS (PV Rapid ShutdownSystem), where the PRVSS is to reduce or shut down energy (i.e.,voltage/current) at a location(s) in the PVRSE under certaincircumstances, with an aim toward safety. As another example, anuninsulated live part involving a risk of electric shock or electricalenergy-high current levels shall be located, guarded, or enclosed toprotect against unintentional contact by personnel who may be called onto activate the actuating device while the PV equipment is energized. Asstill another example, the requirements state that within 30 seconds ofan actuator signal, a PVRSS shall maintain controlled conductors at alimit of not more than 30 VDC, or 15 VAC, 8 A and may not exceed 240volt-amperes.

Given the preceding, there arises a need to address certain safetyissues in the proliferation of PV systems, and the preferred embodimentsare directed to such a need as further explored below.

BRIEF SUMMARY OF THE INVENTION

In a preferred embodiment, there is a photovoltaic system. The systemcomprises an inverter, at least one solar panel for providing electricalpower, and electrical wiring for coupling electrical power from the atleast one solar panel to the inverter. The system also comprises atransmitter for transmitting a messaging protocol along the electricalwiring, where the protocol includes a multibit wireline signal. Thesystem also comprises circuitry for selectively connecting theelectrical power from the at least one solar panel along the electricalwiring to the inverter in response to the messaging protocol.

Numerous other inventive aspects and preferred embodiments are alsodisclosed and claimed.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 illustrates an electrical block diagram of a PV system accordingto a preferred embodiment.

FIG. 2 illustrates a messaging protocol with a single message forcontrolling connectivity of all solar panels.

FIG. 3 illustrates an exemplary view of a single Keep-Alive signalKAS_(x) from FIG. 2.

FIG. 4 illustrates a flowchart of a preferred embodiment method 20 ofoperation of each receiver RC_(x) to sample signals on grid GR so as todetect the presence, or lack thereof, of a stream of Keep-Alive signalsand to respond appropriately.

FIG. 5 illustrates a flowchart of a preferred embodiment method fordetecting the presence of, preferably consecutive, Keep-Alive signalsand the appropriate response of reactivating a connection between asolar panel SP_(x) and grid GR.

FIG. 6 illustrates an alternative methodology for detecting Keep-Alivesignals and either enabling or disabling the connectivity of a solarpanel SP_(x) to grid GR according to a majority decoding methodology.

FIG. 7 illustrates an alternative messaging protocol of an ongoingstream of Keep-Alive signals, with groups of S 15-bit Keep-Alive signalsand each signal differs in its binary values from the other signals inthe group.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 illustrates an electrical block diagram of a photovoltaic (PV)system 10, according to a preferred embodiment. System 10 includesvarious aspects known in the art which are first described here,followed by additional preferred embodiment aspects described in theremainder of this document. Looking first to the former, system 10includes a number N of solar panels, shown by way of example in FIG. 1as solar panel SP₁, panel SP₂, . . . , through panel SP_(N). Each solarpanel is connected, typically by parallel electrical connection, to arespective maximum power point tracker (MPPT) MP₁, MP₂, . . . , MP_(N).As is well known, each solar panel SP_(x) is operable to convertincident solar energy (i.e., from the sun) to a DC voltage, and eachsuch MPPT MP_(x) is a DC to DC converter that optimizes the matchbetween each solar panel SP_(x) and the rest of an electrical grid GRthat connects the energy from multiple panels together and to otherdevices connected to grid GR. Further, grid GR connects the plurality ofMPPTs in a wired fashion, shown as a serial connection in FIG. 1, andthe total potential provided by the collective serial path is connectedto an inverter 12. Inverter 12 converts the DC voltage provided from thesolar panels/MPPTs to an AC signal, ν_(AC), where the latter istypically output at a level (e.g., 110 volts AC) to accommodate thevoltage requirements of equipment or devices that will use theelectricity generated by system 10. Lastly, note that various otheritems are known in the art and may be connected to the electrical gridof FIG. 1, including batteries; such items are not shown in FIG. 1,however, to focus the discussion on remaining preferred embodimentaspects described below.

Looking to additional preferred embodiment aspects of system 10, itswireline connection is further enhanced to include apparatus forwireline network communications so as to achieve rapid shutdown, andcontrolled reactivation, of electrical connectivity to each of solarpanels SP₁ through SP_(N). In this regard, inverter 12 includes a safetyactuator 12 _(SA), which may be an electrical, mechanical, or graphicaloperable button or interface that, when actuated, will commence aprocess to interrupt the supply of electricity from a solar panelSP_(x), or more than one solar panel, to grid GR. Further in thisregard, safety actuator 12 _(SA) may be a user-operated control, such asby an administrator or other personnel who, for safety purposes, desiresto remove the electrical provision from a solar panel SP_(x) to grid GR,such as when responding to an emergency or comparable situation thatinvolves system 10. As another example, safety actuator 12 _(SA) may besoftware and/or hardware that detects a condition and, in response yetwithout user-intervention, operates safety actuator 12 _(SA) so as toinstigate the solar panel electrical shutdown process; for example, sucha condition may be a detected arc or electrical spike. Moreover, safetyactuator 12 _(SA) also is operable to control the re-connection orreactivation of power supply from one or more solar panels to grid GR.Thus, as detailed below, safety actuator 12 _(SA) along with othercircuitry provides selective connectivity as between solar panel energyand grid GR, whereby in some instances the connection between the two isenabled and electricity couples between the two, while in otherinstances the connection between the two is interrupted so thatelectricity is not coupled between the two.

Further in the preferred embodiment, a transmitter 12 _(T) is associatedwith inverter 12, such as being incorporated inside the housing ofinverter 12 or connected to the same wireline connections of inverter12, where for sake of example in FIG. 1 transmitter 12 _(T) is shownconnected in parallel to the conductors connected to inverter 12.Transmitter 12 _(T), as further detailed below, is operable to transmitsignals along grid GR so as to facilitate the function of safetyactuator 12 _(SA), that is, when safety actuator 12 _(SA) is to commencea shutdown or reactivation of a solar panel connection to grid GR, thentransmitter 12 _(T) communicates appropriate signaling to achieve such aresult. Further in this regard, each of solar panel SP₁, SP₂, . . . ,SP_(N)incorporates, or is connected to, a respective receiver RC₁, RC₂,. . . , RC_(N). Thus, a receiver RC_(x) also may be incorporated insidethe housing of its respective solar panel SP_(x) or connected to thesame wireline connections of that panel, where for sake of example inFIG. 1 each such receiver RC_(x) is shown connected in parallel to theconductors connected to its respective solar panel SP_(x). In general,transmitter 12 _(T), and each of the receivers RC₁, RC₂, . . . , RC_(N),may be constructed with various hardware and software, as ascertainableby one skilled in the art, so as to achieve the functionality includingcommunications and protocol described in this document.

Each receiver RC_(x) is also shown with a control connection (by way ofan arrow) to a respective MPPT MP_(x); for example, receiver RC₁ has acontrol connection to MPPT MP₁, MP₂, and so forth. By this control, eachreceiver may signal its respective MPPT to electrically isolate itsrespective solar panel SP_(x) from providing electricity to grid GR; forexample, receiver RC₁ may control MPPT MP₁ so that solar panel SP₁cannot provide current to inverter 12. In this regard, therefore,switching circuitry is included in each MPPT MP_(x), whereby theconnectivity from the solar panel SP_(x), through the MPPT MP_(x) and toinverter 12, may be interrupted, such as through an open circuit (e.g.,relay, switch, or other element for preventing current flow). Likewise,such circuitry may be controlled to reconnect or reactivate this opencircuit so as to restore electrical power provision by a solar panelSP_(x) to grid GR.

Operation of safety actuator 12SA of inverter 12 to control solar panelconnectivity is accomplished in a preferred embodiment by a messagingprotocol between inverter 12 and either the solar panels or some othercircuitry, where in a preferred embodiment such circuitry are the MPPTs,that can open/close the connectivity between a solar panel (or group ofpanels) and grid GR. In one preferred embodiment, the messaging protocoluses a singular message to control all solar panels, while in analternative preferred embodiment, different messages according to aprotocol correspond to respective groups of one or more panels, whereeach group will respond to its respective signal. Each of thesealternatives is described below.

FIG. 2 illustrates a messaging protocol with a single message forcontrolling connectivity of all solar panels. As shown in FIG. 2,transmitter 12 _(T) preferably communicates the messaging protocol alongthe wireline connectivity of FIG. 1, as an ongoing stream of what willbe referred to herein as Keep-Alive signals. As a wirelinecommunication, various of the complexities and costs associated with thealternative of wireless communications is avoided. In any event, acontinuous stream of Keep-Alive signals are shown in FIG. 2,sequentially following one another in time, where each such signal isalike, that is, contains the same information as the other such signals.As further detailed later, each receiver RC_(x) evaluates signalingalong the connections to that receiver so as to detect such Keep-Alivesignals, and as long as such detection occurs with sufficiency overtime, the receiver RC_(x) control to its respective MPPT_(x) is suchthat the corresponding solar panel SP_(x) continues to supply current togrid GR. However, if a receiver RC_(x) fails to detect a sufficientquantity of such Keep-Alive signals during a given period of time, thenthe receiver RC_(x) controls its respective MPPT_(x) so as to disconnectits respective solar panel SP_(x) from supplying current to grid GR. Inthe latter instance, therefore, safety considerations such as thosearising from the NEC can be achieved, by quickly, efficiently, andreliably shutting down the receipt of power by grid GR from a solarpanel SP_(x).

FIG. 3 illustrates an expanded view of a single Keep-Alive signalKAS_(x) from FIG. 2. In a preferred embodiment, each Keep-Alive signalKAS_(x) is a 15 bit signal (shown as bits b₀ through b₁₄), where eachbit is communicated across a 5 millisecond (ms) duration, so that theentire Keep-Alive signal KAS_(x) transmission period is 75 ms. Moreover,each bit is preferably transmitted by transmitter 12 _(T) usingfrequency shift keying (FSK) modulation. As known in the FSK art, eachof the binary values is transmitted at a differing frequency, where the1 is called the mark frequency f_(M) and the 0 is called the spacefrequency f_(S), where such frequency differentiation improves propersignal detection if one of the frequencies is more susceptible to poorchannel quality. Additionally, when the channel is limited by randomadditive noise, an SNR improvement of 10 log₁₀(15)=11.8 dB is obtainedby encoding the Keep-Alive signal into a 15-bit sequence as shown inFIG. 3, where preferably the sequence is pseudo-orthogonal with respectto any random sequences. Still further, note that each Keep-alive signalconsists solely of data bits, with no overhead required to limitdifferent portions of a packet or frame, such as a separate header,payload, and possible accuracy check (e.g., CRC) or other frameterminating field. Accordingly and as detailed below, each of thereceivers RC_(x) evaluates grid GR for a signal presence at either offrequencies f_(M) and f_(S) to thereby detect an incoming Keep-Alivesignal. Moreover, where in one preferred embodiment the Keep-Alivesignals are transmitted without a pause or time space between successivesignals and with a continuous phase transition, then a correlator may beimplemented in each receiver RC_(x). Thus, with knowledge of the bitpattern of the Keep-Alive signal, then should the Keep-Alive signalarrive within a 75 ms window of time, a peak will be detected by thecorrelator when autocorrelation is high, thereby confirming the presenceof the Keep-Alive signal. As further detailed below, such a signaldetection will maintain the connectivity of a solar panel SP_(x), orgroup of solar panels, to grid GR. Moreover, with continuous phasetransition, note that such detection may occur without any additionalsynchronization or messaging overhead as between transmitter 12 _(T) andthe receivers RC₁ through RC_(N).

FIG. 4 illustrates a flowchart of a preferred embodiment method 20 ofoperation of each receiver RC_(x) to sample signals on grid GR so as todetect the presence, or lack thereof, of a stream of Keep-Alive signalsand to respond appropriately. Method 20 commences with a system startstep 22, illustrating start-up of system 10 according to principlesknown in the art. Accordingly, assuming proper operation, then in step22 each solar panel SP_(x) provides electrical energy to itscorresponding MPPT MP_(x), and with any power conversion needed of thesolar-panel-provided energy as also known in the art, each correspondingMPPT MP_(x) provides a corresponding electrical signal to grid GR.Meanwhile, assuming no activation of safety actuator 12 _(SA), theninverter 12 provides an ongoing sequence of recurrent Keep-Alivesignals, as shown in FIG. 2, to grid GR. Next, method 20 continues fromstep 22 to step 24.

In step 24, each receiver RC_(x) initiates to zero a parameter shown asFAIL COUNT. As its name suggest, the parameter FAIL COUNT represents acounter for reach receiver RC_(x), indicating a count of the number oftimes that the receiver RC_(x) fails to detect the presence of aKeep-Alive signal. After step 24, method 20 continues to step 26.

In step 26, each receiver RC_(x) samples grid GR in an effort to detectthe presence of a Keep-Alive signal. In a preferred embodiment, thesample period of step 26 is equal to the transmission period of theKeep-Alive signal, which in the example of FIG. 3 is 75 ms. Thus, step26 determines whether a Keep-Alive signal is detected in 75 ms and, asintroduced earlier, one manner of such detection is by performing acorrelation in the receiver using the known 15-bit sequence of theKeep-Alive signal with FSK bits detected at either the f_(M) or f_(S)frequencies. Next, method 20 continues from step 26 to step 28.

In step 28, each receiver RC_(x) determines whether its preceding step26 decoding operation detected a valid Keep-Alive signal during themonitored transmission period. If the correlation locates an adequatepeak within the sampled transmission period thereby indicating such adetection, then the method flow returns from step 28 to step 24. Thuswhen a receiver detects a single valid Keep-Alive signal, the FAIL COUNTis again reset to zero, and the next decoding step repeats. If, however,step 28, determines that the step 26 decoding step failed to detect avalid Keep-Alive signal during the monitored transmission period, thenmethod 20 continues from step 28 to step 30.

In step 30, each receiver RC_(x) increments its FAIL COUNT parameter byone. For example, therefore, if FAIL COUNT was formerly a value of zero,such as for a first instance of steps 26 and 28, then following step 30FAIL COUNT will equal one. As introduced earlier, therefore, theparameter FAIL COUNT continues to keep a count of a number of successivetransmission periods where a valid Keep-Alive signal is not detected. Asshown above, however, when FAIL COUNT is non-zero and a valid Keep-Alivesignal is detected, then such an event produces an affirmative findingin step 28 and causes FAIL COUNT to reset to zero. To the contrary, eachtime FAIL COUNT is incremented, next a step 32 is performed, todetermine if FAIL COUNT exceeds some integer threshold THR1, where thevalue of THR1 may be selected by one skilled in the art, for exampleafter empirical testing of system 10. If step 32 determines that FAILCOUNT does not exceed THR1, then method 20 returns from step 32 to step26, with FAIL COUNT therefore then being greater than zero. To thecontrary, if step 32 determines that FAIL COUNT equals (or exceeds)THR1, then method 20 continues from step 32 to step 34.

From the preceding, one skilled in the art should appreciate that step34 is reached only when a successive number of transmission periods(e.g., 75 ms intervals) equal to THR1 are sampled by a receiver RC_(x),and for each such period a valid Keep-Alive signal is not detected.Under such conditions, in step 34 the receiver RCs signals itsrespective MPPT MP_(x) to disable the connectivity between itsrespective solar panel SP_(x) and grid GR. Thus, in summary, method 20demonstrates that in one preferred embodiment, each receiver RC_(x)samples signaling on grid GR, and if a number equal to THR1 sequentialtransmission periods occur without the receiver detecting a validKeep-Alive signal, then the solar panel SP_(x) corresponding to thatreceiver is thereby prevented from providing energy to grid GR. Withthis understanding, and returning to FIG. 1, note therefore that whennormal full power-generation of system 10 is desired, then transmitter12 _(T) continuously transmits Keep-Alive signals as shown in FIG. 2,but when safety actuator 12 _(SA) is activated to disconnect power togrid GR, then transmitter 12 _(T) discontinues the transmission ofKeep-Alive signals; in response, once a number of transmission periodsequal to THR1 elapse without a Keep-Alive signal having been transmittedduring that entire duration, each MPPT MP_(x) is signaled to prevent itscorresponding solar panel SP_(x) from providing energy to grid GR. Thus,activation of safety actuator 12 _(SA) in this manner will timely andefficiently cause the disruption of power to grid GR from one or moresolar panels, in just over the time to detect the entire duration ofTHR1 times the Keep-Alive signal transmission period.

As another aspect of a preferred embodiment, structure and functionalityare included so as to reactivate a connection between solar panels andgrid GR, following a disconnection from an incidence of step 34. In thisregard, reactivation is controlled via inverter 12 and its associatedtransmitter 12 _(T), where for example safety actuator 12 _(SA) mayinclude an additional control, button, interface, or event, whereuponactivation of any of these attributes transmitter 12 _(T) willre-commence sending Keep-Alive signals along grid GR, and upon receiptof a sufficient number of these signals within a predetermined period,solar panel energy that was formerly disconnected from grid GR isre-established. In this regard, FIG. 5 illustrates one preferredembodiment method 40 consistent with the above, which is now discussed.

FIG. 5 illustrates a flowchart of a preferred embodiment method 40 ofoperation of each receiver RC_(x) that is comparable in numerousrespects to method 20 of FIG. 4, so FIG. 5 is discussed in less detailas the reader is assumed familiar with the earlier discussion. In method40, again each receiver RC_(x) samples signals on grid GR to detect thepresence, or lack thereof, of a stream of Keep-Alive signals. In method40, however, the presence of, preferably consecutive, Keep-Alive signalswill be detected and the appropriate response of reactivating aconnection between solar panel SP_(x) and grid GR will be achieved.

Method 40 commences with a system start step 42, illustrating start-upof system 10 after a solar panel SP_(x) has been disconnected fromsupplying energy to grid GR in accordance with method 20 of FIG. 4.Thereafter, in step 44, a receiver RC_(x) corresponding to thedisconnected solar panel SP_(x) initiates to zero a parameter shown asSUCCESS COUNT. As its name suggest, the parameter SUCCESS COUNTrepresents a counter for reach receiver RC_(x), indicating a count ofthe number of times that the receiver RC_(x) successfully detects thepresence of a Keep-Alive signal. After step 44, method 40 continues tostep 46.

Step 46, and the step 48 following it, perform the same functionality assteps 26 and 28 of FIG. 4. Thus, in step 46 a receiver RC_(x) samplesgrid GR to detect the presence of a Keep-Alive signal over thetransmission period of that signal, and in step 48 a receiver RC_(x)determines whether its preceding step 46 decoding step detected a validKeep-Alive signal during the monitored transmission period. In step 48,however, the direction of flow is reversed, relative to step 28, basedon either a negative or affirmative determination of the step 48condition. In other words, if in step 48 no Keep-Alive signal wasdetected in the preceding step 46, then method 40 returns to step 44 andthe SUCCESS COUNT is reset to (or remains at) zero, and the decodingstep 46 repeats. If, however, step 48, determines that the step 46decoding step indeed detected a valid Keep-Alive signal during themonitored transmission period, then method 40 continues from step 48 tostep 50.

In step 50, a receiver RC_(x) increments its SUCCESS COUNT parameter byone. Thus, the parameter SUCCESS COUNT keeps a count of a number ofsuccessive transmission periods where a valid Keep-Alive signal isdetected, following a time where the solar panel SP_(x) corresponding tothe receiver RC_(x) was disconnected from grid GR. Each time SUCCESSCOUNT is incremented by a step 50, next a step 52 is performed, todetermine if SUCCESS COUNT exceeds some integer threshold THR2, wherethe value of THR2 may be selected by one skilled in the art, again forexample after empirical testing of system 10, but where preferably THR2of step 52 is greater than THR1 of step 32 from FIG. 4. If step 52determines that SUCCESS COUNT does not exceed THR2, then method 40returns from step 52 to step 46, with SUCCESS COUNT therefore then beinggreater than zero. To the contrary, if step 52 determines that SUCCESSCOUNT equals (or exceeds) THR2, then method 40 continues from step 52 tostep 54.

From the preceding, one skilled in the art should appreciate that step54 is reached only when successive a number of transmission periods(e.g., 75 ms intervals) equal to THR2 are sampled by a receiver RC_(x),and for each such period a valid Keep-Alive signal is detected. Undersuch conditions, in step 54 the receiver RC_(x) signals its respectiveMPPT MP_(x) to enable or reactivate the connectivity between itsrespective solar panel SP_(x) and grid GR. Thus, in summary, method 40demonstrates that in one preferred embodiment, after a solar panelSP_(x) has been disconnected from grid GR, then its correspondingreceiver RC_(x) samples signaling on grid GR, and if a successive numberequal to THR2 of Keep-Alive signals are detected, then the solar panelSP_(x) corresponding to that receiver RC_(x) is thereby reconnected toprovide energy to grid GR. Thus, recalling that safety actuator 12 _(SA)is operable to re-commence sending Keep-Alive signals along grid GRafter a panel has been disconnected from the grid, method 40 thereforewill, upon receipt of a sufficient number of these signals within apredetermined period, reconnect a solar panel SP_(x) to provide energyto grid GR where that connection was formerly disconnected.

FIG. 6 illustrates an alternative preferred embodiment methodology fordetecting Keep-Alive signals and either enabling or disabling theconnectivity of a solar panel SP_(x) to grid GR, that is, as analternative to methods 20 and 40 of FIGS. 4 and 5, respectively. By wayof introduction, whereas methods 20 and 40 operate in response to eachsuccessive Keep-Alive signal transmission period and control may bealtered based on a single Keep-Alive signal (e.g., as received in step26 or failed to be received in step 46), method 60 performs a majoritydecoding process over an odd number Z of Keep-Alive signal transmissionperiods, whereby the majority of detected signals, or lack thereof,during the Z periods, causes the resultant control to either connect ordisconnect a solar panel SP_(x) with respect to grid GR. Examples ofspecific steps to achieve such functionality are described below.

Method 60 commences with a system start step 62, illustrating an initialdefault state of system 10, which could be established such that allsolar panels are connected (i.e., via respective MPPTs) to grid GR, oralternatively for a safety mode could be such that all solar panels aredisconnected from grid GR. Next, in step 64, each receiver RC_(x)initiates to zero an index parameter shown as Z, and method 60 continuesto step 66. In step 66, each receiver RC_(x) samples grid GR in aneffort to detect the presence of a Keep-Alive signal, in the same manneras described earlier for step 26 (or step 46). Then, in step 68, theindex parameter Z is incremented, after which method 60 continues tostep 70.

Step 70 is a conditional step so that overall method 60 will analyze atotal number of sample periods (i.e., transmission periods) equal to anodd number value shown as THR3. Thus, step 70 determines whether step 66has been repeated a total of THR3 times, where if the total is notreached, method 60 loops back to decode another transmission period andagain increment the index Z, and once the total of THRE3 is reachedmethod 60 continues to step 72.

In step 72, each receiver RC_(x) performs a majority decode on the THR3samples periods that have been decoded by repeated instances of step 66,so as to determine whether the majority of those periods detected avalid Keep-Alive signal. In other words, since THR3 is an odd number,then step 72 determines whether a majority of the transmission periodsin the THR3 transmission periods were occupied by a valid Keep-Alivesignal. For example, if THR3 is 9 periods, then step 72 determines if atleast 5 of those periods (i.e., ROUNDUP(THR3/2)=ROUNDUP(9/2)=5)presented a valid Keep-Alive signal. If the majority of the THR3 periodsdetected a valid Keep-Alive signal, then method 60 continues to step 74,which like step 54 in FIG. 5, controls an MPPT MP_(x) to enable theconnectivity of the corresponding solar panel SP_(x) to grid GR. Inopposite fashion, if the majority of the THR3 periods failed to detect avalid Keep-Alive signal, then method 60 continues to step 76, which likestep 44 in FIG. 4, controls an MPPT MP_(x) to disable the connectivityof the corresponding solar panel SP_(x) from grid GR. After either step74 or step 76, method 60 continues to a step 78, which provides anadditional fail-safe evaluation. Specifically, step 78 determineswhether a number of on/off transitions from alternate occurrences ofsteps 74 and 76 have occurred in less than some time period threshold;if this has occurred, such transitioning may be cause for concern and,as a result, method 60 continues from step 78 to step 80, which likestep 76, disables connectivity of the corresponding solar panel SP_(x)from grid GR due to the relatively frequent on/off transitions (whereone skilled in the art may select an appropriate number and time periodthreshold for step 78). To the contrary, if step 78 does not detect suchrepeated transitions, method 60 returns to step 64, whereupon a next setof THR3 transmission periods may be analyzed in a comparable manner asdescribed above.

With method 60, one skilled in the art may choose the value of Z given atradeoff in that the larger the value of Z, the longer amount of timerequired before step 72 is reached, that is, the larger the value of Z,the greater amount of time will elapse between actuation of safetyactuator 12 _(SA) and the responsive action of either step 74 or step76. Specifically, such amount of time will be at least equal to Z timesthe Keep-Alive signal transmission period (e.g., 75 ms). In accordancewith the preferred embodiments, therefore, Z is either equal to seven ornine, as testing has indicated that error production for such numbersshould be sufficient. Specifically, such testing considers potentialerrors in the operation, such as a first error where a solar panelSP_(x) remains connected undesirably after transmission of theKeep-Alive signal ceases, or such as a second error where a solar panelSP_(x) is reconnected to grid GR even though a sufficient number ofKeep-Alive signals have not been transmitted. Testing, however, isbelieved to predict that for Z=9, a chance of such an error is only onepercent during many centuries (if not longer) of operation.

The above has described how each receiver RC_(x) responds to a samesingular 15-bit code (e.g., FIG. 3) to cause either connection ordisconnection of a respective solar panel SP_(x) to grid GR, but recallearlier mentioned is that an alternative preferred embodiment providescontrol of groups of solar panels. In this regard, FIG. 7 illustrates analternative messaging protocol, whereby to maintain solar panelconnectivity to grid GR, transmitter 12 _(T) again communicates alongthe wireline connectivity of FIG. 1 an ongoing stream of Keep-Alivesignals, but in FIG. 7 the stream includes groups of S 15-bit Keep-Alivesignals, where each of the S signals in a group preferably has a sametransmission duration (e.g., again, 75 ms) but differs in its binaryvalues from the other signals in the group, preferably selected from aset of pseudo-orthogonal signals, and where each such signal is forcontrolling a separate set of one or more MPPTs (and the gridconnectivity of their corresponding solar panels). For example, assumethat S=4, then FIG. 7 is intended to illustrate that in a firsttransmission period of S transmission periods, a first Keep-Alive signalKAS_(1.1) is transmitted, followed in continuous phase transition by asecond Keep-Alive signal KAS_(1.2), followed by a third and so forth upthrough the S^(th) (i.e., fourth) Keep-Alive signal KAS_(1.S), for atotal duration of S times the individual Keep-Alive signal transmissionperiod of time (i.e., 4*75 ms=300 ms). Thereafter, the entire sequenceof S Keep-Alive signals is re-transmitted, and so forth, so long asconnectivity is desired as between each group of solar panels and gridGR.

Given the sequence of FIG. 7, the alternative preferred embodimentmodifies any of FIGS. 4, 5, and 6, whereby each receiver RC_(x) performsits decoding step only with respect to the 15-bit sequence that isassigned to that particular receiver. For example, assume that system 10includes a total of eight solar panels SP₁ through SP₈, where the solarpanels are paired with respect to a controlling Keep-Alive signal; thus,as an example, panels SP₁ and SP₂, and their respective receivers RC₁and RC₂, are responsive to the first Keep-Alive signal KAS_(1.1), whilepanels SP₃ and SP₄, and their respective receivers RC₃ and RC₄, areresponsive to the second Keep-Alive signal KAS_(1.2), and so forth, asshown in the following Table 1:

TABLE 1 Solar panel, Controlling receiver Keep-Alive signal SP₁, RC₁KAS_(1.1) SP₂, RC₂ KAS_(1.1) SP₃, RC₃ KAS_(1.2) SP₄, RC₄ KAS_(1.2) SP₅,RC₅ KAS_(1.3) SP₆, RC₆ KAS_(1.3) SP₇, RC₇ KAS_(1.4) SP₈, RC₈ KAS_(1.4)

Given the controlling signals as shown in Table 1, then each receiverRC_(x) performs its decoding step (i.e., either 26, 46, or 66) for aduration equal to S times the individual signal transmission period(e.g., 300 ms), so as to determine if its individual 75 ms signal isdetected during that same time. Because the preferred embodimentimplements pseudo-orthogonal bit sequences in the set of S Keep-Alivesignals, a satisfactory correlation detection should be provided foreach of the different signals. Beyond this change, any of methods 20,40, or 60 may be followed, applying the remaining steps with respect toa receiver and its corresponding Keep-Alive signal. For example, in theinstance of Table 1, receiver RC₁, if performing method 60, will attemptto locate Keep-Alive message KAS_(1.1) during a first 300 ms interval,after which the Z index is incremented and the process repeats untilTHR3 such 300 ms intervals are sampled; thereafter, receiver RC₁ willcontrol MPPT MP₁ to either connect solar panel SP₁ to grid GR if themajority of Z sampling periods decoded a valid Keep-Alive messageKAS_(1.1) or it will control MPPT MP₁ to disconnect solar panel SP₁ fromgrid GR if the majority of Z sampling periods failed to locate a validKeep-Alive signal KAS_(1.1) during that interval. Meanwhile, during thissame time interval, the other receivers will likewise operate withrespect to their respective Keep-Alive signals. For example, receiverRC₈, while also performing method 60, will attempt to locate Keep-Alivemessage KAS_(1.4) during the same first 300 ms interval in whichreceiver RC₁ is sampling for Keep-Alive message KAS_(1.1), after whichthe Z index is incremented and the process repeats until THR3 such 300ms intervals are sampled; thereafter, receiver RC₈ will control MPPT MP₈to either connect solar panel SP₈ to grid GR if for the interval themajority of Z sampling periods decoded a valid Keep-Alive messageKAS_(1.4), or it will control MPPT MP₈ to disconnect solar panel SP₈from grid GR if for the interval the majority of Z sampling periodsfailed to locate a valid Keep-Alive signal KAS_(1.4) during that period.One skilled in the art should readily appreciate the comparableoperation of the remaining receivers and respective MPPT/panels, inimplementing any of methods 20, 40, or 60.

Given the preceding, the preferred embodiments provide an improved PV(solar panel) system operable to disconnect or reactivate connectivityof such panels to a power grid, for instance in connection with safetyconsiderations. While various aspects have been described,substitutions, modifications or alterations can be made to thedescriptions set forth above without departing from the inventive scope.For example, while system 10 includes one receiver per solar panel/MPPTpair, in an alternative preferred embodiment a single receiver could beused to control multiple MPPTs, and the solar panel connectivity tothose MPPTs. As another example, while the messaging protocol has beenshown to provide bits for enabling solar panel connectivity to the grid,such bits, or alternative sets of bits, also may be used to provideadditional commands. As still another example, while method 60 isdescribed in connection with sampling successive time periods of Z timesthe Keep-Alive signal transmission period, in an alternative preferredembodiment a sliding window of time may be used such that the mostrecent THR3 sample periods are analyzed in connection with the majoritydecoding decision. As still another example, various of the flowchartsteps may be re-ordered or further modified (including adding additionalsteps), and sizing of parameters may be adjusted, such as changes to anyof signal bit size, transmission period, THR1, THR2, THR3, N, Z, and soforth. Still other examples will be ascertainable by one skilled in theart and are not intended as limiting to the inventive scope, whichinstead is defined by the following claims.

The invention claimed is:
 1. A system comprising: a power source; switching circuitry that includes: a set of inputs coupled to the power source; a set of outputs operable to couple to a DC power grid such that the power source is coupled to the DC power grid via the switching circuitry; and a control input; and a receiver operable to couple to the DC power grid in parallel with the switching circuitry, wherein: the receiver includes a counter and a control output coupled to the control input of the switching circuitry; and the receiver is operable to: monitor for a signal on the DC power grid; increment the counter in response to the signal; reset the counter in response to an absence of the signal; and cause the switching circuitry to couple and decouple the power source from the DC power grid in response to the counter.
 2. The system of claim 1, wherein the signal is in a frequency shift keying (FSK) modulated messaging protocol.
 3. The system of claim 1, wherein the signal encodes a sequence of bits.
 4. The system of claim 3, wherein: the signal is a first signal; the sequence of bits is a first sequence of bits; the receiver is operable to increment the counter in response to the first signal that encodes the first sequence of bits; and the receiver is operable to ignore a second signal on the DC power grid that encodes a second sequence of bits that is different from the first sequence of bits.
 5. The system of claim 4, wherein the first sequence of bits and the second sequence of bits are pseudo-orthogonal.
 6. The system of claim 4, wherein the first signal and the second signal are transmitted without a time space between.
 7. The system of claim 1 further comprising a transmitter operable to couple to the DC power grid and to provide the signal over the DC power grid.
 8. The system of claim 7 further comprising an inverter that includes: a set of inputs operable to couple to the DC power grid in parallel with the transmitter; a set of outputs operable to couple to an AC power grid; and inverting circuitry operable to provide power on the AC power grid using power on the DC power grid.
 9. The system of claim 1 further comprising a DC to DC converter operable to convert a first DC voltage of the power source to a second DC voltage of the DC power grid.
 10. The system of claim 1, wherein the receiver is further operable to: detect a number of transitions of the switching circuitry between coupling and decoupling the power source from the DC power grid within a time period; and cause the switching circuitry to decouple the power source from the DC power grid in response to the number of transitions.
 11. A device comprising: switching circuitry operable to couple a power source to a DC power grid, wherein the switching circuitry includes a control input; and a receiver operable to couple to the DC power grid in parallel with the switching circuitry, wherein: the receiver includes a counter and a control output coupled to the control input of the switching circuitry; and the receiver is operable to: monitor for a signal on the DC power grid; increment the counter in response to a failure to receive the signal; reset the counter in response to receiving the signal; and cause the switching circuitry to decouple the power source from the DC power grid in response to the counter exceeding a threshold.
 12. The device of claim 11 further comprising the power source.
 13. The device of claim 11 further comprising: a transmitter operable to couple to the DC power grid and to provide the signal over the DC power grid; and an inverter operable to: couple to the DC power grid in parallel with the transmitter; couple to an AC power grid; and provide power on the AC power grid using power on the DC power grid.
 14. The device of claim 11, wherein the signal is in a frequency shift keying (FSK) modulated messaging protocol and encodes a sequence of bits.
 15. The device of claim 14, wherein: the signal is a first signal; the sequence of bits is a first sequence of bits; the receiver is operable to increment the counter in response to a failure to receive the first signal that encodes the first sequence of bits; and the receiver is operable to ignore a second signal on the DC power grid that encodes a second sequence of bits that is different from the first sequence of bits.
 16. A device comprising: switching circuitry operable to couple a power source to a DC power grid, wherein the switching circuitry includes a control input; and a receiver operable to couple to the DC power grid in parallel with the switching circuitry, wherein: the receiver includes a counter and a control output coupled to the control input of the switching circuitry; and the receiver is operable to: monitor for a signal on the DC power grid; increment the counter in response to receiving the signal; reset the counter in response to a failure to receive the signal; and cause the switching circuitry to couple the power source to the DC power grid in response to the counter exceeding a threshold.
 17. The device of claim 16 further comprising the power source.
 18. The device of claim 16 further comprising: a transmitter operable to couple to the DC power grid and to provide the signal over the DC power grid; and an inverter operable to: couple to the DC power grid in parallel with the transmitter; couple to an AC power grid; and provide power on the AC power grid using power on the DC power grid.
 19. The device of claim 16, wherein the signal is in a frequency shift keying (FSK) modulated messaging protocol and encodes a sequence of bits.
 20. The device of claim 19, wherein: the signal is a first signal; the sequence of bits is a first sequence of bits; the receiver is operable to increment the counter in response to receiving the first signal that encodes the first sequence of bits; and the receiver is operable to ignore a second signal on the DC power grid that encodes a second sequence of bits that is different from the first sequence of bits. 